Wind turbine blade with a lightning protection system

Abstract

The invention relates to a wind turbine blade with a lightning protection system, the lightning protection system comprises at least one lightning receptor arranged freely accessible in or on the shell unit surface at or in the immediate vicinity of the tip of the blade. The lightning protection system further comprises a lightning down conductor made of electrically conductive material extending within the shell body from the lightning receptor to the root end of the blade. The lightning receptor and the lightning down conductor are electrically connected. The shell body comprises at least a first conductive layer extending along at least a longitudinal part of the lightning down conductor in a transverse distance therefrom. The first conductive layer is electrically isolated from the lightning down conductor and from the lightning receptor, and has a sheet resistance in the range 1-5 Mega Ohm per square.

Description

[0001]This is a National Phase Application filed under 35 U.S.C. 371 as a national stage of PCT / EP2010 / 052904, filed 8 Mar. 2010, and claiming the benefit from European Application No. 09154511.1, filed Mar. 6, 2009, the content of which is hereby incorporated by reference in its entirety.TECHNICAL FIELD[0002]The present invention relates to a wind turbine blade with a lightning protection system, wherein the blade comprises a shell body made of a composite material and comprises a longitudinal direction with a root end and a tip end. The blade further comprises a profiled contour including a pressure side and a suction side, as well as a leading edge and a trailing edge with a chord having a chord length extending there between, the profiled contour, when being impacted by an incident airflow, generating a lift. The lightning protection system comprises at least one lightning receptor arranged freely accessible in or on a surface of the shell body. The lightning protection system f...

AI Technical Summary

Benefits of technology

[0013]According to the invention, this object is achieved by the shell body comprising at least a first conductive layer extending along at least a longitudinal part of the lightning down conductor in a transverse distance therefrom, wherein the first conductive layer is electrically isolated from the lightning down conductor and / or the lightning receptor, and wherein the first conductive layer has a sheet resistance in the range of 1-5 Mega Ohm pr. square. The arrangement of the lightning receptor, lightning down conductor, and conductive layer helps to prevent the build-up of streamers and / or leaders. Providing the blade with the conductive layer lowers the electrical field around the lightning down conductor and lightning receptor during a lightning strike by acting as a parasitic conductor. This minimizes the problem with vertical streamers, which is especially present in connection with positive lightning strikes, which account for about 10% of the strikes. Such streamers and leaders are pre-stages of lightning strikes and thus, preventing their build-up also prevents lightning strikes. Moreover, the necessity of multi-receptors is avoided. If the sheet resistance of the conductive layer is too small, the conductive layer may act as a lightning receptor and increasing the risk of a flashover, potentially damaging the insulation of the lightning down conductor and the wind turbine blade. On the other hand, if the sheet resistance is too large, the influence of the layer on the electric field around the lightning down conductor is insufficient to provide the needed protection. Tests on existing blades with simulated lightning strikes at high negative voltages, corresponding to positive lightning strikes, showed that blades equipped with the new lightning protection system have showed no damages to the blade, thereby fulfilling the requirements in the IEC61400-24 CDV standard. Thus, it was surprisingly found that the addition of the first conductive layers having a relative low conductivity provides a much improved, efficient protection against positive lightning strikes compared to conventional lightning protection systems.

[0044]providing the shell body with at least a first conductive layer extending along at least a longitudinal part of the lightning down conductor in a transverse distance therefrom, wherein the first conductive layer is electrically isolated from the lightning down conductor and / or the lightning receptor, and wherein the sheet resistance of the conductive layer is in the range 1-5 Mega Ohm pr. square. According to this inventive method, an existing wind turbine blade may be protected from flashovers and streamer / leader build-up.

Problems solved by technology

If the sheet resistance of the conductive layer is too small, the conductive layer may act as a lightning receptor and increasing the risk of a flashover, potentially damaging the insulation of the lightning down conductor and the wind turbine blade.

On the other hand, if the sheet resistance is too large, the influence of the layer on the electric field around the lightning down conductor is insufficient to provide the needed protection.

Images